In cable TV (CATV) networks, television signals available at the subscriber's premises at the CATV cabling outlet (CP) are normally further processed by a set-top converter (STC) prior to connection to consumer TV equipment. Unfortunately, various types of consumer TV equipment are not necessarily able to directly select and process the signals coming from the CATV network. Only "cable-ready" consumer TV equipment is able to directly select and process non-scrambled channels. In any case, a set-top converter is necessary for selecting and processing "access-controlled" or premium channels since descrambling and communication functions have to be provided. The typical CATV signal provided at a subscriber's premises consists of a large plurality of AM/VSB television channels (some scrambled and most not scrambled) which are frequency division multiplexed over a very wide frequency band. Of course, each separate television channel is modulated by a different video and audio program.
In the switched video broadband system depicted in copending, co-owned U.S. patent application Ser. No. 07/739,203, now abandoned, and related applications cross-referenced therein, the selected television channels provided at the subscriber's premises are presented in the form of a frequency division multiplex of only six FM TV channels modulated by unscrambled video and audio programming. These six channels are the result of a selection and interdiction process within the network resulting from one or more end user requests from within the subscriber's premises.
The multiplex structure of a signal such as may be provided to the subscriber's premises, according to the above-cited U.S. patent application, is shown in FIG. 1. It shows six fixed channels between 300 and 550 MHz, for example. In copending, co-owned application Ser. No. 07/738,188, now abandoned, six fixed 30 MHz channels occupy a band covering 330 to 510 MHz. A block diagram of a set-top converter that could be used for tuning and demodulating such a band of FM video and sound is shown in FIG. 2.
In the above-cited patent applications a switched video, fiber-to-the-curb system is disclosed in which the six frequency division multiplexed FM modulated TV channels are delivered from an optical network unit (ONU) in a neighborhood of a plurality of subscriber premises. Each of the subscriber premises is provided with a coax drop having up to six TV channels dynamically selected by persons using different displays in each subscriber's premises. Any six FM TV channels can be delivered to each of the subscribers' premises but are always delivered in the same band, e.g., 330-510 MHz covering a total of 180 MHz with 30 MHz dedicated to each channel. The users in each subscriber's premises are individually capable of dynamically selecting channels for occupying the six slots by sending control signals from remote control units to a set-top converter which uplinks the control data back to the upstream switched video control which has access to typically hundreds of video channels. Since the central control can be programmed to recognize particular subscribers' contract data it can be used to block premium channels rather than having a descrambler associated with the set-top converter. Therefore, the channels distributed to the individual subscribers are unscrambled and only a tuner is needed to select from the switched programs distributed among the six fixed frequency channels.
As shown in FIG. 1, the frequency spectrum of such a system might use a selected narrow band 2 in the frequency band below 50 MHz for upstream (uplink) control data from the individual users to the terminal controller and a similarly narrow frequency band 4 greater than 108 MHz for any data downlinked from the terminal controller to the individual subscribers. As mentioned, a fairly wide band of 180 MHz between 300 and 550 MHz is shown in this case for carrying the six FM TV channels, each being about 30 MHz wide, for example.
The set-top converter 10 shown in FIG. 2 may include a display 12 having a channel number display. It may be used to indicate on or standby, stereo/SAP modes, network failure, etc. The display characters may be multiplexed with the video signal prior to driving the TV video output. A keyboard 14 may be used in lieu of a similar keyboard on a remote control unit 16 as a backup in case of a remote control failure. The keyboard may have updown channel selection capability, may be able to turn the set-top converter on or off or standby, and may have a sound volume control and various sound modes.
A remote control receiver 18 receives infrared coded signals 20 from the remote control unit 16. Channel selection is made by pressing an alphanumeric keyboard and/or enter key on the remote control unit 16. It may also have up-down channel selection capability, standby capability, up-down sound volume control, sound muting and various sound modes.
A central processing unit (CPU) 22 receives data from functions and manages the communications with the network. Operational tasks include the transmission of codes related to the remote control and keyboard commands, management of access protocol with the network (CSMA-CD), processing of control data coming from the network such as acknowledgment, STC selection, channel display, etc., and may also be used for maintenance functions.
The CPU interfaces with a data modem 24 on a line 25 (which includes downlinked data on a line 25a and uplinked data on a line 25b ) which interfaces with the two-way RF data channels on a line 27 which multiplexed in the interface 26 on one coaxial cable with the TV channels. The CPU also manages any collisions between data channels from other STC's connected to the home premises cabling.
An input interface 26 enables the establishment of a physical connection with a home cabling RF inlet 28 as well as a bidirectional communication with the network. It performs the coupling between the incoming FM TV channels and incoming and outgoing data channels.
The STC 10 provides RF and baseband video/sound outputs from signals available at the customer port 28. This generic function is performed by a number of functional blocks to be described below.
A tuner 30 selects, converts and filters one of the six wide band FM channels available at the customer port 28 into an intermediate frequency (IF) channel. An FM video demodulator 32 demodulates the FM IF carrier in order to obtain the video and sound contents of FM channels and performs the separation of baseband video and sound subcarrier. The 140 IRE composite video NTSC signal is then split in order to drive a TVAM-modulator 34 for the video display unit, a VCR video baseband output 36 and the set-top converter display 12. The TV AM modulator 34 provides an AM-VSB TV channel with the same carrier frequency as channel 3 or 4. This carrier is modulated by the NTSC signal available from the FM video demodulator 32 and a variable monaural sound signal on a line 38 provided by a sound processor 40. A sound demodulator 42 demodulates the sound subcarrier to obtain the NTSC composite sound signal. This signal is further processed in the sound processor 40 to obtain the baseband sound contents: mono, stereo or SAP.
A power supply 44 provides for DC voltages to various STC hardware from a 110 VAC plug. A power switch (not shown) may be provided on the rear of the STC 10.
As will be clearly understood from the foregoing, the tuner function performs the selection of one channel among the six available at the RF input 28. As in a conventional CATV tuner, this function involves rather complex RF signal conditioning techniques and is therefore fairly expensive, especially the tuner.
One of the common problems a conventional CATV subscriber will meet when using the network is the simultaneous connection to a TV set and a VCR. Since there are no descrambling functions in a VCR, it cannot be directly used to record, except with non-scrambled channels. Therefore, a set-top converter is needed. Dedicated connections are commonly proposed for performing the recording of channels being watched or the recording of channels independently of the TV set status. In the configuration shown in FIG. 3A, for example, a large plurality of network channels are provided on a line 48 to a conventional set-top converter 50. The nature of the signals on the line 48 are typically AM-VSB delivered in a frequency division multiplexed format. Some of the channels will be scrambled and others will be free of scrambling. The tuner will be provided with special descrambling circuits upon payment of a premium by the subscriber. The STC 50 provides an RF output at the frequency corresponding to channel 3, for example, on a line 52. A VCR 54 is connected to the signal on the line 52 at an RF input thereof. The VCR RF output will provide an output signal on a line 56 having the STC channel 3, or channel 3 in VCR playback mode where a tape is being played back. A TV set 58 is responsive to the RF out on the line 56 from the VCR 54 and is tuned to channel 3 to display the selected video program provided on the line 56. The set-up shown in FIG. 3A permits either an unscrambled or scrambled channel to be recorded by the VCR. However, the recording of one channel while another one is watched is not possible if both are scrambled.
FIG. 3B is similar except the VCR is shown upstream of the set-top converter and is therefore only able to record unscrambled channels. Various elaborate wiring schemes are known in the art for allowing the subscriber to select either the TV set or the VCR as the equipment used to record or watch the scrambled channel while the other device is simultaneously used with an unscrambled channel.
If a subscriber wished to record one scrambled channel while watching another scrambled channel, a second set-top converter is needed leading to a rather complicated connection and an excessive cost.
The fiber-to-the-curb system disclosed in the abovecited U.S. patent application Ser. No. 07/739,203 has the same connection problem as the conventional CATV systems described above although it is different in nature. Indeed, the selection and interdiction of channels within the switched video FTC network avoids the need for a descrambler in the set-top converter. Also, since six different set-tops can be used simultaneously within the same subscriber's premises for watching or recording different ones of the six available programs that are selected, a tuner is needed in the set-top converter. This tuner is automatically adjusted by the network, through a dedicated command, to a free channel position from among the six available slots. Unfortunately, since there is only one tuner in the STC 10 of FIG. 2, two set-top converters similar to the one shown in FIG. 2 would be required to record and watch two different channels. Therefore, for a fiber-to-the-curb system, one can draw similar conclusions as those drawn for conventional CATV as described above.